Articles molded of thermoplastic molding compositions, including colored, pigmented and tinted compositions are well known. Also known are processes for dyeing articles by immersion in special pigmenting mixtures. Among the advantages attained by such tinting, especially of lenses, mention has been made of reduced light transmission and mitigation of glare.
U.S. Pat. No. 4,076,496 disclosed dipping an article in a dye bath that contains a dye and as a solvent, a mixture of glycerol and ethylene glycol, optionally with a minor proportion of water or other organic solvent.
U.S. Pat. No. 5,453,100 disclosed polycarbonate materials that are dyed by immersion into a mixture of dye or pigment dissolved in a solvent blend. The blend is made up of an impregnating solvent that attacks the polycarbonate and allows the impregnation of the dye or pigment and a moderating solvent that mitigates the attack of the impregnating solvent. The impregnating solvent thus disclosed includes at least one solvent selected from dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether and propylene glycol monomethyl ether.
PCT/CA99/00803 (WO 0014325) disclosed tinting plastic articles by immersion in an aqueous dispersion and exposing the dispersion and immersed article to microwave radiation.
JP 53035831 B4 disclosed polycarbonate moldings that are dyed in aqueous dispersion containing dispersed dyes and diallyl phthalate, o-phenylphenol or benzylalcohol.
JP 55017156 disclosed aliphatic polycarbonate lenses that are colored with a liquor containing dyes and water.
JP 56031085 (JP-104863) disclosed compositions containing a disperse dye in an aliphatic ketone and polyhydric alcohol said to be useful in coloring polycarbonate films at room temperature.
JP2000248476 disclosed a molded polycarbonate bolt that was dyed with a solution containing dyes, an anionic leveling agent and then treated with a solution containing thiourea dioxide.
U.S. Pat. No. 4,812,142 disclosed polycarbonate articles dyed at a temperature of 200° F. or above in a dye solvent having a boiling point of at least 350° F.
U.S. Pat. No. 3,514,246 disclosed immersing molded polycarbonate articles in an emulsified dye liquor which contains a water insoluble dyestuff, an oil-soluble surface active agent dissolved in an aliphatic hydrocarbon solvent and water. The procedure was repeated with similar results where the surfactant was replaced by a poly(oxyethylene) derivative.
U.S. Pat. No. 3,532,454 disclosed dyeing of polycarbonate fibers with a dye composition that contains at least one of alkoxyalkylbenzyl ether, alkylene glycol di-benzyl ether, benzoic acid alkoxyalkyl ester or phenoxy acetic acid-alkoxyalkyl ester.
U.S. Pat. No. 3,630,664 disclosed a dye bath that required the presence of a carbonate conforming to a specific formula, e.g., ethyl-benzyl-carbonate.
The art, therefore, includes a variety of techniques for tinting molded articles and all the presently relevant ones involve dipping of the article in a hot dye mixture under conditions to promote infusion of the dyes. Once tinted, the article is removed from the solution, rinsed and dried to produce articles ready for commerce.
Several problems may arise in connection with these practices, especially in the instances where large articles are to be colored. In these instances, there is often a need for large volumes of dye solution and the vessel into which the article needs to be dipped must be rigorously reinforced to support the great weight of the article and of the dyeing liquid. Also, the vessel must be equipped with heating means, pumping and ancillary equipment, including piping for circulating the dye solution. To heat hundreds of gallons of solvent to the required temperature, a very large heater is needed for a commercially reasonable operation. Additionally, for some shapes and for large articles, it is necessary to equip the dipping vessel with jets to promote vigorous circulation of the solution so as to achieve uniform tinting. Effective circulation is often difficult to achieve in rectangular-shaped tanks and the resulting tinting is not always uniform. Another problem associated with dipping of large articles for the purpose of tinting is the loss of components of the hot dye solution by evaporation. Finally, in practicing the dip-dye technology, the tinted article needs to be transferred from the dipping vessel to a different area to be water-rinsed and then to a drying step. Moving large articles often requires special equipment to enable transfer and is also wasteful in terms of time and space.
One object of the present invention is to provide an efficient process for the tinting of plastic articles.
Another object of the present invention is to provide a process yielding uniformly tinted articles.